Interpretive Summary: Vitamin D is an essential nutrient for bone health and has shown to significantly reduce the risk of cancers, such as breast and prostrate cancers. However, recent reports have shown that many Americans are deficient in vitamin D, particularly those of dark skin, elderly and infants. Natural food sources for vitamin D are limited to a few animal sources, such as some fish and fish liver oils. A few foods, such as milk, cereal, and some fruit juices are fortified with vitamin D. Additional food sources are needed to help the public meet the required daily intake of vitamin D. After exposure to UV light, mushrooms provide a significant amount of vitamin D in the form of vitamin D2. Investigators at the Processed Foods Research Unit (PFRU) at the WRRC, in Albany, CA, have investigated post-harvest UV-B processing conditions, such as high intensity, dose, and time between harvest and treatment, for the formation of vitamin D2 in Portabella mushrooms, as well as vitamin D2 retention during refrigerated storage. This information will help mushroom producers develop optimum commercial-scale UV-B processing conditions to add value to their mushrooms and improve public health.

Technical Abstract:
The objectives of this research were to study the effects of high intensity (0.5, 0.75, and 1.0 mW/cm2), dose (0.5, 1.0, and 1.5 J/cm2), and post-harvest time (1 and 4 days) on the vitamin D2 formation in Portabella mushrooms (Agaricus bisporus) as a result of UV-B exposure, as well as the vitamin D2 degradation in treated mushrooms during storage. At high intensity, the mushrooms produced over 3.83 µg/g d.s., which was over 280% of the daily value of vitamin D, in 8 minutes. Within each intensity application, dose had the largest effect where more exposure converted more vitamin D2 from ergosterol. Similar dose across each intensity application resulted in similar vitamin D2 concentration. From a processing standpoint, intensity was a major factor where the time it took to achieve similar vitamin D2 concentration for similar dose exposure was significantly reduced as intensity increased. Also, post-harvest time did not have a significant effect on vitamin D2 formation in mushrooms that were treated 1 and 4 days after harvest. Vitamin D2 degraded in treated mushrooms during storage by apparent first-order kinetics, where the degradation rate constant was 0.025 h-1. The information provided in this study will help mushroom producers develop commercial-scale UV treatment processes to add value to their crop while improving consumer health.